Capacitance arrangement and method relating thereto

ABSTRACT

A capacitance arrangement comprising at least one parallel-plate capacitor comprising a first electrode means, a dielectric layer and a second electrode means partly overlapping each other. A misalignment limit is given. Said first electrode means comprises a first and a second electrode arranged symmetrically with respect to a longitudinal axis, said first and second electrodes have a respective first edge, which face each other, are linear and parallel such that a gap is defined there between. Said second electrode means comprises a third electrode with a first section and a second section disposed on opposite sides of said gap interconnected by means of an intermediate section, which is delimited by a function depending on a first parameter and a second parameter. One of said two parameters is adapted to be selected hence allowing calculation of the other parameter to determine the shape and size of the second electrode means.

TECHNICAL FIELD

The present invention relates to a capacitance arrangement whichconsists of at least one parallel-plate capacitor comprising a firstelectrode means, a dielectric layer and a second electrode means whichare substantially disposed in parallel and on either side of saiddielectric layer and which partly overlap each other whereby theequivalent capacitance depends on the size of the overlapping area ofsaid first and second electrode means and wherein a misalignment limitis given defining the maximum allowable extent of misalignment between arespective first and second electrode means. The invention also relatesto a method of fabrication of such a capacitance arrangement.

BACKGROUND

It is a well known fact that it is very difficult, or even impossible,to fabricate capacitors which have exactly the desired capacitance,particularly in the case of parallel-plate capacitor arrangements wherethe overlapping area between a first electrode means and a secondelectrode means gives the capacitance due to allowable misalignmentduring the fabrication process. Thus, it is not possible to guaranteethat the capacitance will be exactly the desired one; it is onlypossible to guarantee that it will fall within a range given by anallowable misalignment, i.e. an allowable misalignment limit. This isclearly disadvantageous since in many cases an exactly definedcapacitance is needed. A particular case relates to so called varactors,i.e. tunable capacitors. Coplanar plate and parallel plate electrodesare for example considered for applications in phase and frequencyagile, i.e. tunable, adaptable, reconfigurable, microwave systems. Incomparison with analogue (semiconductor, MEM) varactors, the varactorsbased on the use of a ferroelectric film have a higher tuning speed, ahigher Q(quality)-factor and lower leakage currents, which is veryadvantageous.

FIG. 1A shows very schematically a coplanar plate varactor arrangement10 ₀₁ wherein two coplanar electrodes 3 ₀₁, 3 _(01′) are deposited ontop of a ferroelectric film 2 ₀₁ which in turn is disposed on asubstrate 1 ₀₁. For the varactor arrangement 10 ₀₁ of FIG. 1A, for agiven ferroelectric film, the capacitance is defined by the shape of theelectrodes and the gap width g between the electrodes 3 ₀₁, 3 _(01′). Inparallel-plate varactors as shown in FIGS. 1B-1F, the ferroelectric filmis instead sandwiched between two electrodes, c.f. FIG. 1B wherein aferroelectric film 2 ₀₂ is disposed between a top electrode 3 _(02′) anda bottom electrode 3 ₀₂ which is disposed on a substrate 1 ₀₂. For agiven ferroelectric film, the capacitance is defined by the thickness tof the ferroelectric film in the area where the top and the bottomelectrodes overlap and by the overlapping area and by the dielectricpermittivity of the film.

FIG. 1C shows an alternative implementation of a parallel-plate varactorarrangement wherein a top electrode 3 _(03′) is disposed on aferroelectric film 2 ₀₃ partly in overlap with a bottom electrode 3 ₀₃disposed on a substrate 1 ₀₃. The varactor arrangement 10 ₀₃ of FIG. 1Chas a capacitance which, for a given ferroelectric film, is given by theoverlapping area which is given by the width w×l+Δl, wherein w is thewidth of the overlapping portion and l+Δl is the length of theoverlapping portion.

FIG. 1D shows still another known parallel-plate varactor arrangement 10₀₄ comprising a substrate 1 ₀₄, a top electrode 3 _(04′) and a bottomelectrode 3 ₀₄ which are disposed on either sides of a ferroelectricfilm 2 ₀₄ such as to partly overlap. A low permittivity film (withdielectric constant ∈<10) 4 ₀₄ is arranged such as to define theoverlapping area, the length portion b where there is no such extra filmdefining the actual relevant portion. A top view of this arrangement isshown in FIG. 1E where it can be seen the width c of the overlappingportion and hence the overlapping area being defined by the opening b×cin the low permittivity film.

In still another parallel-plate arrangement 10 ₀₅ comprising a substrate1 ₀₅, dielectric film 2 ₀₅ lower and upper electrodes 3 ₀₅, 3 _(05′) anopening is formed in the bottom electrode (3 ₀₅) or alternatively in thetop electrode (3 ₀₅) to define an overlapping area A=b×c.

However, all these known varactor arrangements suffer from drawbacks.For example, varactors with coplanar plate electrodes as shown in FIG.1A have a simple design but they require application of higher voltagesthan parallel-plate varactor arrangements, typically the requiredvoltage is above 50-100V. Varactors with parallel-plate electrodes asshown in FIG. 1B-1C do not require such high voltages but typically itis enough with a voltage of 5-20V, but on the other hand it is adisadvantage of such designs that they are sensitive to the alignment ofthe top and the bottom electrodes during the fabrication process.Normally a ferroelectric film with an extremely high permittivity isused and due to this extremely high permittivity, which typically isabove 100, a small disalignment Δl (c.f. FIG. 1C) will result insubstantial changes in the capacitance, which make the prediction of thecapacitance non-controllable and hence the design of the arrangementwill not be cost-effective. The design shown in FIG. 1D, 1E offers agood capacitance prediction but it requires more masks and fabricationprocesses making them cost ineffective. The arrangement shown in FIG. 1Foffers a comparatively good capacitance prediction but it isdisadvantageous in so far that extra ohmic losses are associated withstrips connecting the leads or pads of the capacitor of the overlappingarea of the parallel-plate structure.

SUMMARY

What is needed is therefore a capacitance arrangement for which thecapacitance can be predicted to a high extent. Moreover a capacitancearrangement is needed which has a simple design and which still does notrequire, particularly in the case of a varactor arrangement, highvoltages. Most particularly a capacitance arrangement or varactorarrangement is needed which to a high degree is insensitive to anymisalignment. Basically a capacitance arrangement or a varactorarrangement is needed through which the capacitance is controllable.Still further a varactor arrangement is needed which is easy and costefficient to fabricate. Still further such a capacitance arrangement isneeded which does not suffer from high ohmic losses due to the design.

In other words, a capacitance arrangement is needed which has low ohmiclosses or a high Q-factor associated with the electrodes and which doesnot require many masks and processing steps hence enabling a costeffective fabrication. Particularly a parallel-plate varactor orcapacitance arrangement is needed for which the effective overlap areais not sensitive to any misalignment that may be introduced during thefabrication.

Therefore, a capacitance arrangement as initially referred to isprovided wherein a first electrode means comprises a first and a secondelectrode arranged symmetrically with respect to a longitudinal axis.Said first and second electrodes have a respective first edge, whichrespective first edges face each other, are linear and parallel suchthat a gap is defined there between. The second electrode meanscomprises a third electrode which comprises a first section and a secondsection disposed on opposite sides of said gap and inter-connected bymeans of an intermediate section which is delimited by a first curvededge and a second curved edge. Said first and second curved edges aresymmetrical and oppositely directed with respect to said longitudinalaxis. The shape of said intermediate section is given by a function F(x)which contains a first parameter and a second parameter. One of saidparameters is adapted to be selected, allowing calculation of the otherparameter such that the capacitance of the capacitance arrangement willbe misalignment invariable within the given misalignment limit.

Particularly the said first parameter (k) determines the shape or thecurvature of F(x) (and size) and the second parameter (A) is half thewidth of the second electrode means, i.e. the third electrode. In anadvantageous implementation the first parameter k is adapted to beselected allowing calculation of the second parameter A which normallyis easier. Of course, the inventive concept also covers the case whereinthe second parameter is selected and the first parameter calculateddepending on said selection. Particularly the first and secondelectrodes are adapted to have a shape and to be arranged such that theoverlapping area gives a predetermined capacitance independently of anyoccurring misalignment (Δx) within the given misalignment limit givingdifferent overlaps in the region of the intermediate section on the sideof the first section and of the second section, i.e. the overlappingarea will not be symmetric with respect to an axis perpendicular to thelongitudinal axis in the middle of the first and second electrode.

Most particularly the capacitance between the first electrode and thethird electrode is proportional to the sum of the overlap of the firstelectrode and the first section of the third electrode, the overlapbetween the first electrode and the intermediate section in the absenceof any misalignment, and the first misalignment overlap area (ΔS₁),wherein the first electrode and the intermediate section in thelongitudinal direction limited by the maximum allowed misalignment. Thecapacitance between the second electrode and the third electrode isproportional to the sum of the overlapping area of the second electrodeand the second section of the third electrode, the overlap between thesecond electrode and the intermediate section in absence of anymisalignment and a second misalignment overlapping area (ΔS₂) of thesecond electrode and the intermediate section in the oppositelongitudinal direction limited by the maximum allowed misalignment. Saidfirst and second misalignment overlapping areas have opposite signs,i.e. if the first misalignment overlapping area has a positive sign, thesecond has a negative sign or vice versa. Particularly said first andsecond parameters are so selected and calculated respectively that therelationship between the first and the second misalignment overlapareas, ΔS₁, ΔS₂, or between corresponding first and second capacitancedifferences ΔC₁, ΔC₂, will be such that the equivalent capacitance ofthe arrangement is independent of any produced misalignment, within thegiven misalignment limit.

Particularly the first misalignment overlapping area ΔS₁ is equal to theoverlapping area of a first section S1 divided by the quotient betweenthe overlapping area of a first section and the second misalignmentarea, S1/ΔS₂ minus 2, i.e. ΔS1=S1/((S1/ΔS₂)−2). Particularly the shapeof the intermediate section is given by a function F(x)=A·e^(kx),wherein 2A is the width of the second electrode means, i.e. twice thefirst parameter and k being the first parameter defining the slope orcurvature, wherein 0<x<2Δx_(A), Δx_(A) being the misalignment limit.Particularly half of the width of the second electrode means isA=−k·S1/(e^(kWg/2)), wherein S1 is the overlapping area of a firstsection, Wg being the gap width and k being the parameter determiningthe slope or curvature of the function delimiting the intermediatesection. Particularly the first and second sections are symmetrical. Thefirst and second sections may be square shaped, rectangular,semicircular or partly irregular.

In a most particular implementation a number of capacitors(parallel-plate capacitors or varactors) are connected in series. In oneembodiment the second electrode means comprises a bottom electrode andthe first electrode means comprises a top electrode, or vice versa.Alternatively the first or the second electrode means may be disposed ona substrate although this is not necessarily the case.

In one embodiment the dielectric material has a low or comparatively lowdielectric constant, for example consisting of SiO₂ or a material withsimilar properties, the arrangement being a non-tunable capacitancearrangement. In an alternative embodiment it comprises a varactorarrangement and the dielectric layer comprises a ferroelectric layerwith a tunable dielectric constant which preferably is high or veryhigh.

The dielectric layer may then for example comprise a tunable ceramicmaterial such as SrTiO₃, BaSTO or a material with similar properties.The electrode means generally consists of a metal such as Au, Ag, Pt,Cu.

The ferroelectric or dielectric material may comprise a thin film, i.e.thin film technology may be implemented. However, the invention is notlimited to thin film implementations but the dielectric or ferroelectriclayer may also comprise a thick film.

It is an advantage of the invention that circuits, particularlycapacitors or varactors, can be fabricated having precisely oraccurately defined capacitance values. It is a major advantage thatparallel plate capacitors or varactors which are, to a high degree,insensitive to misalignments between the top and bottom electrodes thatmay be produced during the fabrication process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be further described, in anon-limiting manner, and with reference to the accompanying drawings, inwhich:

FIG. 1A schematically shows a state of the art capacitor/varactorarrangement of the coplanar type,

FIG. 1B schematically illustrates a first parallel-plate varactor orcapacitor arrangement according to the state of the art,

FIG. 1C shows another example of a state of the art parallel-platecapacitor or varactor arrangement,

FIG. 1D is a cross-sectional, schematical view of still another state ofthe art parallel-plate capacitor/varactor arrangement,

FIG. 1E is a top view of the parallel-plate varactor arrangement of FIG.1D,

FIG. 1F shows still another parallel-plate capacitor/varactorarrangement according to the state of the art,

FIG. 2 illustrates a first embodiment of a capacitor/varactorarrangement according to the present invention when there is nomisalignment between the first and the second electrode means,

FIG. 2A is a simplified circuit representation of the arrangement ofFIG. 2,

FIG. 3 illustrates a capacitor/varactor arrangement as in FIG. 2 butwhere there has been a misalignment between first and second electrodemeans,

FIG. 3A is a simplified circuit representation of the misalignmentarrangement of FIG. 3,

FIG. 4 schematically illustrates an alternative embodiment acapacitor/varactor arrangement according to the invention,

FIG. 5 shows very schematically still another embodiment of a varactorarrangement according to the invention,

FIG. 6 very schematically illustrates an arrangement according to theinvention with varactors connected in series,

FIG. 7 illustrates an example of a quarter of an electrode structureobtained for a misalignment invariant varactor according to theinvention, and

FIG. 8 shows an alternative example of an electrode structure (aquarter) obtained for a misalignment varactor according to anotherimplementation.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGS. 1A-1E showing arrangements have been discussed above under thebackground section and will therefore not be further discussed herein.

According to the present invention the top and/or bottom electrodes areso shaped in relation to each other that the effective overlapping areawill be unsensitive to any misalignment (within a predetermined maximummisalignment limit). The arrangements according to the differentembodiments can be made as capacitance arrangements or as varactorarrangements, i.e. comprising a tunable capacitor. For the reasons ofsimplicity will in the following mainly be referred to varactors but itshould be clear that it may just as well be capacitors, the differencelying in the dielectric constant of the thin or thick film on eithersides of which first and second electrode means are disposed.

FIG. 2 shows a first embodiment of a varactor arrangement 10 accordingto the present invention. In FIG. 2 the lay-out is presented for a casewhere there actually is no misalignment between the electrodes on eithersides of the ferroelectric layer. A first electrode means comprising afirst electrode 4 ₁ and a second electrode 4 ₂ are disposed on a thinferroelectric film (not shown in the figure). It is here supposed thatthe first and second electrodes 4 ₁, 4 ₂ are rectangular or squareshaped and disposed symmetrically with respect to a longitudinal axis xsuch that a gap of a width w_(g) is provided between them. They arehence symmetrically located both with respect to the longitudinal axis xand to an axis y perpendicular to the axis x and parallel with thelongitudinal extension of the gap. Since there is no misalignment thisaxis y is supposed to be in the middle of the gap. On the other side ofthe ferroelectric film a second electrode means comprising a thirdelectrode 3 is disposed. It comprises a first electrode section 3 ₁ anda second electrode section 3 ₂ which have the same shape and which herealso are supposed to be symmetrically disposed with respect to thelongitudinal axis x. In this particular embodiment they are supposed tobe square shaped but they may have substantially any shape as will beshown below. An intermediate section 3 ₃ interconnects said first andsecond sections 3 ₁, 3 ₂. The shape of the intermediate section 3 ₃ isdetermined by a function F(x) which is to be appropriately establishedas will be more thoroughly described below. The equivalent capacitanceof the arrangement is given by the overlapping areas which here are thesame, i.e. the part of the first and second electrodes 4 ₁, 4 ₂overlapping first and second sections 3 ₁, 3 ₂ of the second electrodemeans and, since there is no misalignment, the symmetrical and identicaloverlapping areas of the intermediate section 33 and the first andsecond electrodes 4 ₁, 4 ₂. Thus, in FIG. 2 two metallized interfacescomprising the first and second electrode means 4 ₁, 4 ₂, 3 areprecisely aligned forming the varactor 10, established by a seriesconnection of two similar varactors, c.f. FIG. 2A, due to twooverlapping areas S1, S2 which here are similar. Each varactor has anominal capacitance

${C\; 1^{\prime}} = {{C\; 2^{\prime}} = {\frac{ɛ_{r}ɛ_{0}S\; 1}{h} \equiv {C\; 1}}}$wherein S1 denotes the respective overlapping areas, and h the thicknessof the ferroelectric film in the overlapping area.

FIG. 2A is a simplified circuit representation of a first varactorcomprising the varactor formed by the overlapping area between the firstelectrode 4 ₁ and the first section 3 ₁ of the third electrode 3 andpart of the intermediate section 3 ₃ connected to the first section 3 ₁identical to the area S1 and correspondingly C2 is the capacitance ofthe varactor formed by the second electrode 4 ₂ and the second section 3₂ and the corresponding part of the intermediate section 3 ₃ connectedto said second section. In this case they are identical.

FIG. 3 shows the topology of the same arrangement as in FIG. 2 but wherethere is a misalignment Δx between the first and the second electrodemeans. As can be seen from the figure, the effect of the misalignmentwill differ for the two varactors. In the figure Δx illustrates themisalignment. As can be seen the first electrode means comprising theelectrodes 4 ₁ and 4 ₂ has been displaced a distance Δx on thelongitudinal axis x. The misalignment area also called the capacitancearea of the first varactor is increased, the increase being indicatedΔS1 in the figure, and C1≡S1+ΔS1. For the other varactor, on the otherhand, the capacitance is decreased by ΔC2, i.e. C2≡S1−ΔS2, which meansthat for the first varactor, in this case, the capacitance is increasedwhereas it for the other is decreased. In the figure ΔS1 indicates themisalignment area for the first varactor and ΔS2 indicates themisalignment area for the second varactor. Generally ΔS1 is not equal toΔS2. The total capacitance C of the two varactors is 1/C=1/C1+1/C2.According to the present invention the relationship between ΔC1 and ΔC2is established so that the total capacitance or equivalent capacitanceof the misalignment capacitor is the same as the total capacitancewithout misalignment, i.e. it should be the same for the varactorarrangement of FIG. 2 as for the varactor arrangement of FIG. 3. Theformula above can be written:

$\frac{S\; 1}{2} = \frac{( {{S\; 1} + {\Delta\; S\; 1}} ) \times ( {{S\; 1} - {\Delta\; S\; 2}} )}{( {{S\; 1} + {\Delta\; S\; 1}} ) + ( {{S\; 1} - {\Delta\; S\; 2}} )}$which can be simplified to ΔS1=S1/((S1/ΔS2)−2).

This gives the relationship between ΔS1 and ΔS2 that is needed for thevaractor arrangement of FIG. 2 and FIG. 3 to have the same or similartotal area capacitance S1/2. This relationship can be used to find afunction F(x) defining the shape of the electrodes. In general thefunction may be represented by different shapes, and assume differentforms. Here one example of a function is given as S(x)=Ae^(kx), wherein0<x<2×Δx_(A), Δx being the maximum misalignment of the metallicinterfaces or between the first and the second electrode means. ΔS1 andΔS2 can then be specified in an analytic form as:ΔS1=A(e ^(k(Wg/2+Δx)) −e ^(k(Wg/2)))/k and ΔS2=A(e ^(kWg/2) −e^(k(Wg/2−Δx)))/k.S1 can then be obtained as S1=−2Ae^(kWg/2)/k.

It should be noted that in the last formula there is no dependence onΔx, i.e. on the misalignment. This actually means that by properlyestablishing A and k a thoroughly misalignment independent capacitancecan be obtained, i.e. a varactor for which the capacitance isindependent with respect to any misalignment of the first and secondelectrode means. Properly here means that the last formula(S1=2A(e^(kWg/2))/k) is satisfied.

As can be seen there are two different parameters, A and k, which meansthat one of them can be selected as independent. Generally it is mostconvenient to select the value for k, since A then can be calculatedanalytically as:A=−kS1/(2e ^(kWg/2))

If instead A is selected a transcendental equation with respect to k hasto be solved. 2A corresponds to the width of the second electrode means.

In the following an example will be given describing the designing ofthe shape of the electrodes in the range of a possible maximummisalignment such that the capacitance will be completely misalignmentindependent. First, it is here supposed that a value of k is selectedwhich is such that the widths of the electrodes (A) is reasonable.Subsequently the area of the electrodes is adjusted so that the desiredcapacitance given S1 is obtained. In a particular embodiment it issupposed that an alignment invariant capacitance is designed which hasan equivalent area of 25 μm². It is supposed that the gap between theelectrodes is 4 μm and the possible misalignment is +/−2 μm. k is herethen selected to be −0.49/w_(g), which gives A=5 μm. A program can beused to plot the shape of the electrodes and FIG. 7 shows a symmetricquarter of an electrode structure obtained with the above figures.

FIG. 8 is a figure similar to FIG. 7 for another design where theelectrodes or particularly the first and second electrodes sections ofthe second electrodes means are of a more general shape instead ofrectangular though their areas are similar.

FIG. 4 is a figure similar to FIG. 3 showing a varactor arrangement 20where a second electrode means 3′ comprising a first electrode section 3₁′ and a second electrode section 3 ₂′ connected by an intermediatesection 3 ₃′ arranged on a substrate 1′ on top of which of adielectrical ferroelectric film is arranged, upon which a firstelectrode means comprising a first electrode 4 ₁′ and a second electrode4 ₂′ is disposed such that an overlap is given corresponding to S1′+ΔS1′and S2′−ΔS2′ respectively. However, since there is a misalignmentpresent, Δx, the misalignment areas ΔS₁′ and ΔS₂′ are not the same (cf.FIG. 3). The difference actually here is that the first and secondelectrode sections 3 ₁′, 3 ₂′ are substantially semicircular, or have anoval shape.

FIG. 5 shows still another embodiment of a varactor arrangement 30wherein a second electrode means comprising a first electrode section 3₁″ and a second electrode section 3 ₂″ interconnected by means of aintermediate section 3 ₃″ is disposed on a substrate arranged such as toprovide an overlap with a first electrode means comprising a first and asecond electrode 4 ₁″, 4 ₂″ which sections are rectangular and arrangedas the structure in FIG. 2, i.e. symmetrically along a longitudinal axisx but with a misalignment where the misalignment area ΔS₁″ and ΔS₂″ arenot equal. In this case the first and second electrode sections arerectangular instead of semicircular or squareshaped or similar. In anyother aspect the functioning is the same as that described withreference to FIGS. 2 and 3 and the figure is merely included toexplicitly illustrate that different shapes can be used.

FIG. 6 very schematically shows a varactor arrangement 40 comprising twovaractors 3 ₁₀, 3 ₂₀, 30 ₃₀ connected in series. This means that twovaractors, i.e. parallel-plate varactors, are disposed on a substrate 1₁₀ with a dielectric or ferroelectric film arranged between first andsecond electrode means as discussed above. Due to a misalignmentoverlapping areas are given as S₁₀+ΔS₁₀; S₂₀−ΔS₂₀; S₃₀−ΔS₃₀ and S₄₀+ΔS₄₀respectively. It should be clear that this figure is very schematical,the only intention thereof being to illustrate that several capacitorsformed by first and second electrode means as discussed above, etc. canbe used which are arranged to provide a misalignment invariablearrangement.

It should be clear that the invention can be varied in a number of wayswithin the scope of the appended claims.

1. A capacitance arrangement, comprising: at least one parallel-platecapacitor having: a first electrode means; a dielectric layer; and asecond electrode means substantially in a parallel manner disposed oneither side of said dielectric layer and partly overlapping each other;wherein the equivalent capacitance of the capacitance arrangement isdependent on the size of the overlapping area of said first and secondelectrode means and a misalignment limit defining the maximum allowableextent of misalignment between a respective first and second electrodemeans being given; wherein said first electrode means further comprisesa first and a second electrode arranged symmetrically with respect to alongitudinal axis, that said first and second electrodes each have arespective first edge, which respective first edges face each other, arelinear and parallel such that a gap is defined therebetween; whereinsaid second electrode means further comprises a third electrode, saidthird electrode having a first section and a second section disposed onopposite sides of said gap and interconnected by means of anintermediate section which is delimited by a first curved edge and asecond curved edge which first and second curved edges are symmetricaland oppositely directed with respect to said longitudinal axis, and theshape of which being given by a function (F(x)) depending on a firstparameter (k) and a second parameter (A) and in that one of said twoparameters is adapted to be selected hence allowing calculation of theother parameter to determine the shape and size of the second electrodemeans such that the capacitance of the capacitance arrangement will bemisalignment invariable within the misalignment limit.
 2. Thecapacitance arrangement according to claim 1, wherein the firstparameter (k) determines the shape or curvature of F(x) and in that thesecond parameter (A) is half the width (2A) of the second electrodemeans, being the third electrode.
 3. The capacitance arrangementaccording to claim 2, wherein the first parameter (k) is adapted to beselected allowing calculation of the second parameter (A).
 4. Thecapacitance arrangement according to claim 1, wherein the first andsecond electrodes have a shape and are arranged such that theoverlapping area provides a predetermined capacitance independently ofany misalignment (Δx) within the given misalignment limit (Δx_(A))giving different overlaps of the first electrode means and theintermediate section on the side of the first section and of the secondsection.
 5. The capacitance arrangement according to claim 1, whereinthe capacitance between the first electrode and the third electrode isproportional to the sum of the overlap of the first electrode and thefirst section of the third electrode, the overlap between the firstelectrode and the intermediate section in absence of any misalignment,and a first misalignment overlap area (ΔS1), the first electrode and theintermediate section in the longitudinal direction limited by themaximum allowed misalignment (Δx), and in that the capacitance betweenthe second electrode and the third electrode is proportional to the sumof the overlap area of the second electrode and the second section ofthe third electrode the overlap between the second electrode and theintermediate section in absence of any misalignment, and a secondmisalignment overlap area (ΔS2) of the second electrode and theintermediate section in the opposite longitudinal direction limited bythe maximum allowed misalignment, the first and the second misalignmentoverlap areas having opposite signs, i.e. if the first misalignmentoverlap area has a positive sign, the second has a negative sign or viceversa.
 6. The capacitance arrangement according to claim 5, wherein thefirst and second parameters are selected and calculated respectivelythat the relationship between the first and the second misalignmentoverlap areas (ΔS1,ΔS2), or between corresponding first and secondcapacitance differences (ΔC1,ΔC2), are such that the equivalentcapacitance of the arrangement is independent of any misalignment withinthe given misalignment limit.
 7. The capacitance arrangement accordingto claim 6, wherein the first misalignment overlap area (ΔS1) is equalto the overlapping area of a first or second electrode and a first orsecond electrode section of the second electrode means in absence of anymisalignments (S1) divided by the quotient between said overlapping areaand the second misalignment area (S1/ΔS2) minus 2, i.e.ΔS1=S1/((S1/ΔS2)−2).
 8. The capacitance arrangement according to claim1, wherein the shape of the intermediate section is given byF(x)=A·e^(kx), 2A being the width of the second electrode means, i.e.twice the second parameter, and k being the first parameter defining theslope or curvature wherein O<x<2Δx_(A), Δx_(A) being the misalignmentlimit.
 9. The capacitance arrangement according to claim 1, wherein halfthe width of the second electrode means is A=−k·S1/(e^(k·Wg/2)), S1being the overlapping area of a first/second electrode and afirst/second electrode section in absence of misalignment, Wg being thegap width and k being the first parameter determining the slope orcurvature of the function delimiting the intermediate section.
 10. Thecapacitance arrangement according to claim 1, wherein the first sectionand the second section are symmetrical.
 11. The capacitance arrangementaccording to claim 10 wherein the first section and the second sectionare square shaped, rectangular, semicircular or partly irregular. 12.The capacitance arrangement according to claim 1, wherein the secondelectrode means comprises a bottom electrode and in that the firstelectrode means comprises a top electrode.
 13. The capacitancearrangement according to claim 1, wherein the first or the secondelectrode means is disposed on a substrate.
 14. The capacitancearrangement according to claim 1, wherein the dielectric material has alow dielectric constant consisting of SiO₂ or a material with similarproperties.
 15. The capacitance arrangement according to claim 1,further comprising a varactor arrangement.
 16. The capacitancearrangement according to claim 15, wherein the dielectric layercomprises a ferroelectric layer with a tunable dielectric constant whichis preferably high or very high.
 17. The capacitance arrangementaccording to claim 15, wherein the dielectric layer comprises a tunableceramic material, including SrTiO₃, Ba STO or a material with similarproperties.
 18. The capacitance arrangement according to claim 1,wherein the first and second electrode means is a metal selected fromthe group consisting of Au, Ag, Pt, and Cu.
 19. The capacitancearrangement according to claim 1, wherein the wherein the dielectriclayer comprises a thin film ferroelectric material.
 20. The capacitancearrangement according to claim 1, wherein the dielectric layer comprisesa thick film ferroelectric layer.
 21. The capacitance arrangementaccording to claim 1, further comprising a number of parallel platecapacitors or varactors connected in series.
 22. A method for producinga capacitance arrangement comprising at least one parallel-platecapacitor having a first electrode means, a dielectric layer and asecond electrode means wherein said first and second electrode meanspartly overlap each other, the size of the overlapping area giving theequivalent capacitance of the arrangement and wherein further anallowable misalignment limit is given defining the maximum allowableextent of misalignment between a respective first and second electrodemeans, comprising the steps of: establishing an equivalent capacitanceto be provided; determining an allowable misalignment limit; anddesigning a first electrode means comprising two substantiallysymmetrical electrodes with two respective first edges facing eachother, being linear, parallel and adapted to be arranged symmetricallyon a longitudinal axis such that a gap is formed between them, and asecond electrode means comprising a third electrode comprising a firstand a second section located on opposite sides of said gap andinterconnected by means of an intermediate section, by finding afunction F(x), said function F(x) and said function F(x) mirrored insaid longitudinal axis (−F(x)) determining the shape of saidintermediate section on the opposite sides of said longitudinal axissuch that the equivalent capacitance will be misalignment invariablewithin the given misalignment limit.
 23. The method according to claim22, wherein the function F(x) further depends on two parameters one ofwhich being the width (2A) of the intermediate section, the other beingthe slope (k) of the function F(x), and in that the method furthercomprises the steps of: selecting the value of one of said parameters;and calculating the value of the other of said parameters using theselected parameter value.
 24. The method according to claim 23, whereinthe function F(x) is given by F(x)=Ae^(kx) and in that the methodfurther comprises the steps of: selecting the width (w_(g)) of the gap;selecting k; finding the overlapping area (S1) in absence ofmisalignment of the first and second electrode means and the first,second and third sections of the second electrode means respectivelysuch that the desired equivalent capacitance is obtained; andcalculating A as A=−k·S1/e^(k·Wg/2).
 25. The method according to claim22, further comprising the step of disposing the first and secondelectrode means on either sides of a dielectric layer.
 26. The methodaccording to claim 22, further comprising the step of disposing thefirst and second electrode means on either sides of a ferroelectriclayer with a variable dielectric constant to provide a varactorarrangement.
 27. The method according to claim 26, further comprisingthe step of using a photolithographic process to fabricate the capacitoror varactor arrangement.